The present invention relates to polymer-based electroluminescent devices, and more particularly, to display devices constructed from a class of precursors that are electrochemically polymerized to form an electrically conducting polymer that may can be used for the electroluminescent layer in such devices.
Polymer-based electroluminescent devices (PLEDs) have the potential for providing inexpensive alternatives to alpha-numeric displays and x-y addressable displays. PLEDs also have the potential to provide an alternative to back lighted, liquid crystal displays. A simple PLED may be constructed from an electroluminescent layer sandwiched between an electron injection electrode and a hole injection electrode. The electroluminescent layer is typically constructed by depositing a conjugated or conductive polymer on one of the electrodes. Devices based on poly(p-phenylenevinylene) (PPV), or derivatives thereof, have been demonstrated with sufficient quantum yields to be commercially attractive. More complicated devices utilize electron and hole transport layers between the above mentioned electrodes and the electroluminescent layer. The electroluminescent layer generates light when holes and electrons recombine in the layer.
The deposition and patterning of the electroluminescent layer present significant technical problems that must be overcome before economically attractive devices can be fabricated. If the conjugated polymer is soluble in a solvent, a thin film can be made by the spin-coating of a polymer solution. While spin-coated polymer films having good electro-optical properties can be obtained in this manner, the adhesion of spin-coated film to the underlying layer is often insufficient. In addition, many attractive polymers are not sufficiently soluble to be applied via spin-coating.
Spin-coating and other processes in which the entire substrate is coated, present additional problems in multi-color displays in which different xe2x80x9cpixelsxe2x80x9d must be coated with different polymers. The deposition of each layer requires a three-step procedure consisting of a masking step to protect areas that are not to be coated, the spin-coating step, and a mask removal step. In addition to the increased complexity of the masking steps, the solvents utilized with conventional masking systems are often incompatible with the polymers being deposited. Accordingly, it would be advantageous to provide a system that does not require such masking operations.
Broadly, it is the object of the present invention to provide an improved method for fabricating an electroluminescent display.
It is another object of the present invention to provide a method that does not require the masking operations discussed above.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
The present invention is a display device and a method for fabricating the display device. A display device according to the present invention is fabricated from an electrode layer that includes a plurality of electrodes on a substrate. The electrode layer is immersed in a solution of a first precursor polymer in a first solvent. The first precursor polymer includes a plurality of electrochemical polymerizable monomers. Each monomer has first and second polymer-forming active sites that can be joined by electrochemical polymerization and third and fourth polymer-forming active sites that can be joined chemically in solution. The first precursor polymer is soluble in the first solvent whereas a first polymer formed by electrochemical polymerization of the first and second polymer-forming active sites is insoluble in the first solvent. A layer of the first polymer is deposited on the a first one of the electrodes by connecting that electrode to an electric circuit while leaving the others of the electrodes disconnected from the circuit. The electrode is then immersed in a solution of said first precursor polymer. The circuit applies a potential to the electrode sufficient to cause the first and second polymer active sites to polymerize by electrochemical polymerization thereby depositing a first polymer layer includes the first polymer precursor on the first one of the electrodes. A second electrode layer is then deposited over the first polymer layer. In multi-color displays, the different polymer layers corresponding to the various colors are deposited on different ones of the electrodes by sequentially depositing each polymer layer in a similar manner.